One who misrepresents the Constitution is said not to be a "strict constructionist", not a judicial activist.
(Strictly speaking, a judicial activist is a judge that overturns legislation. I used the term loosely.)
I've never heard that definition. The word "activist" got applied to judges because their actions were reminiscent of political activists, only clothed in more patrician garb. IOW, they had an agenda to pursue, and were using their position of power in the courts to pursue it. A judge who holds himself to an objective, unchanging standard - that is, to the law itself - therefore cannot be considered a judicial activist.
"Strict constructionism" is something different. It's someone who has his own rule of interpretation when reading the Constitution (namely, that all of its provisions should be read "strictly"). This may blind him to its actual meaning, since there are some provisions of the Constitution that likely were intended to be read more broadly than others. A judge who does his job properly will not have any preconceived notions as to what the document says or how specifically it is to be read, but will instead read it with an honest eye towards coming to the most accurate conclusion he can about its meaning, based on the text, and the history, principles, and logic behind it.